Molded articles produced using a fiber-reinforced resin composition including a thermoplastic resin and reinforcing fibers are easily molded and processed by virtue of the characteristics of the thermoplastic resin, do not require a load in storage unlike thermosetting resins, and are excellent in recyclability. As these molded articles, those in a variety of forms are known such as thermoplastic prepregs in which reinforcing fibers are arranged in the form of a sheet, and pellets in which reinforcing fibers are randomly dispersed. Molded articles including reinforcing fibers and a thermoplastic resin are excellent in balance between lightness and dynamic characteristics, and are therefore widely used as structural members of aircraft, automobiles, watercraft and the like, electronic equipment housings, sporting goods, and industrial materials such as building materials.
Among thermoplastic resins, a polyarylene sulfide is particularly excellent in heat resistance and chemical resistance so that a molded article produced using the resin can be expected to be applied as an alternative to a metal material. However, when a molded article produced using a polyarylene sulfide is used as an alternative to a metal material, further improvement in the dynamic characteristics, particularly the tensile strength, of the molded article is desired. This is because since the tensile elongation of a general polyarylene sulfide is lower than the tensile elongation of reinforcing fibers, and interfacial bondability between the polyarylene sulfide and reinforcing fibers is low, the reinforcing effect of reinforcing fibers cannot be sufficiently utilized in the molded article.
General means to improve the tensile strength and elongation of a molded article is enhancement of the elongation of a polyarylene sulfide. However, the tensile elongation of a polyarylene sulfide correlates to its molecular weight and, hence, its melt viscosity and, when the tensile elongation of the polyarylene sulfide is improved, the melt viscosity increases so that moldability in production of a molded article may be considerably impaired. It is well known that it becomes harder to combine a polyarylene sulfide with reinforcing fibers as the melt viscosity of the polyarylene sulfide increases. In that case, it is necessary to make the process temperature higher and therefore a polyarylene sulfide is not suitable for easily producing a molded article and a molding material with high productivity. For these reasons, it is an important technical challenge to secure both the tensile strength and molding processability in a molded article produced using a polyarylene sulfide.
In view of the above-mentioned situations, techniques have been disclosed in which the bending characteristic of a molded article is improved by a molding material obtained by sizing to carbon fibers a compound mainly including an epoxy resin and containing a specific catalyst in a molding material including a polyarylene sulfide and carbon fibers as an attempt to improve dynamic characteristics. In those techniques, attempts are made using various forms of reinforcing fibers (Japanese Patent Laid-open Publication Nos. 2013-117003, 2013-117001 and 2013-117000). However, in those techniques, a certain improvement in dynamic characteristics is achieved, but for dynamic characteristics, only the bending characteristic is considered and, in addition, it is not considered that the elongation of a polyarylene sulfide and the state of dispersion of reinforcing fibers in a molded article considerably influence tensile characteristics useful as design parameters for a product. It is predicted that further improvement of the strength is required in application development which will increasingly progress in future.
As a technique with attention given to electrical characteristics and dynamic characteristics among the characteristics of a molded article, an injection-molded article including a polyphenylene sulfide and carbon fibers has been disclosed (Japanese Patent Laid-open Publication No. 8-325385). In the technique disclosed in JP '385, attention is given to the length of fibers in the molded article and the strand strength of carbon fibers, but the resin characteristics of the polyphenylene sulfide that serves as a matrix resin are not considered, and it is absolutely necessary that the dynamic characteristics (bending characteristic) be improved in terms of strength in the application development in future.
Japanese Patent Laid-open Publication No. 11-21457 describes an example of modification of a polyarylene sulfide. The purpose is to improve the adhesiveness of the resulting composite material itself, and the resin properties and processability of a polyphenylene sulfide that serves as a matrix resin are not considered. Further, the composite material shown in examples has a tensile strength of only 129 to 158 MPa, which is insufficient to use the composite material as an alternative to a metal material.
Japanese Patent Laid-open Publication No. 8-59303 discloses a composite material including reinforcing fibers treated with a surface modifier, and a thermoplastic resin, and the tensile characteristics thereof. However, the resin characteristics and processability of a polyphenylene sulfide as a matrix resin are not considered, and the tensile strength of the resulting composite material is insufficient for using the composite material as an alternative to a metal material.
It could therefore be helpful to provide a molded article having a sufficiently high tensile strength with high productivity by specializing the state of reinforcing fibers in the molded article and the characteristics of a polyarylene sulfide as a matrix resin.